LACTIC ACID
FERMENTATION
Lactic acid fermentation is the process of
degradation of the feast to lactic acid. As a
result glycolizis (in anaerobic conditions), a
molecule of glucose receive two molecules
piruvat , which is reduced to lactic acid
molecule. Place in muscles, where oxygen,
which supplied the blood is not sufficient to
meet the energy needs of the body. The
process is done in some bacteria and fungi.
Lactic acid
Glucose
NAD
ATP
2 NAD.H2
piruvat
lactat
(Lactobacillus delbrueckii subspecies bulgaricus)
Lactobacillus Bulgaricus is one of the bacteria
involved in lactic acid fermentation. (Another
is Streptococcus termophilus - the only harmful
to human streptococcus bacterium).
Lactobacillus bulgaricus refers to
homofermentative lactobacillus. Bacterium
cells have stick forms with width below 2
mkm. Grow at 45o C, even at 50-53o C.
Optimum temperature for growth is 40-43o C.
Any change in the composition of the
environment and temperature cultivation
causes changes in morphological and
physiological characteristics of the species.
Lactobacillus Bulgaricus was called after Bulgaria which was first discovered and used. Bacterium
occurs naturally free of Bulgaria. In falling in milk
and under certain conditions Lactobacillus
Bulgaricus (and Streptococcus termophilus) causing
natural lactic acid fermentation, resulting in
obtaining what we call yogurt.
Streptococcus Thermophilus( Streptococcus Salivarius
subsp. Thermophilus) is other bacteria involved in lactic
acid fermentation. It is the only
Safer for human alpha-haemolytic streptococcus
bacterium, which does not form spores.They are
classified as lactic acid bacteria (MKB).The bacteria are
used to produce yogurt, when it is not probiotic, and
don`t survive in the stomach.
Bacterium cells are spherical or oval shaped
with a diameter 0,7-0,9 mkm. It is located in
pairs in the short and long chains. Its optimal
temperature for growth is between 40 and 45o
C. Then it increases at 50o C, but stops
increasing at 53o C. It doesn`t grow below 20o
C.
Products of lactic acid
fermentation
Lactobacillus bulgaricus has been reported for the
first time in 1905. This is done by the Bulgarian
Stamen Grigorov , student , in a report presented
to the Institute “Pasteur” in Paris. It explores
microflora of the Bulgarian yogurt and discovers
that yogurt is produced due to a stick and a globe
bacteria. Later the stick bacteria is called
Lactobacillus bulgaricus, a globe one Streptococcus thermophilus.The origin of the
bacteria is plants. It is believed that due to animal
contact with plants during grazing, bacteria clog
the animal's udder when milking and they fall in
milk. Thus, this makes possible the fermentation
of milk.
Yogurt
Yogurt is milk product which is produced by
fermentation of milk. There are two main
organisms that are involved in fermentation of
yogurt-Lactobacillus bulgaricus and
Streptococcus thermophilus, which are in
simbiotic relationship and this connection
between the two bacteria is beneficial for their
survival and efficiency only when they are
together. The fermentation is not possible in
the presence of a single bacterium. Each of the
two bacteria have a role in fermentation .
Fermentation ends naturally, by cooling.
During the stay in a warm place for a few days
(outside the refrigerator) fermentation
continues, milk spoils and the taste becomes
unpleasantly sour.
History of yogurt
Accurate data about the origin of the Bulgarian
yogurt lacks. One of the theories about its
occurrence is associated with the Thracians.
Ancient Thrace own fertile soil and rich vegetation
succulent pastures. All this contributed to
development ruddy sheep. And because of that
the main domestic animal was sheep. Thracians
noticed that sour milk can be kept fresh for a long
time. By adding the sour milk to the fresh boiled
milk , they received leavened product known as
milk or “prokish” .
Another theory is associated with
proto-Bulgarians . It is that Bulgarian yogurt
goes back to lactic acid drink "kumiss” , which
proto-Bulgarians prepared from mare`s milk.
Once settled in our land and domesticated
sheep began to make "kumiss" from sheep's
milk. Proto-Bulgarians produced yogurt as
well under the name "katak”, as fresh sheep
milk curdle with dilution of cheese. This
product is usually ready by the end of the
summer, when milk has a high content of dry
matter.
Yogurt has a higher nutritional value than fresh
milk. Reason for this are the changes under the
action of Lactobacillus bulgaricus and Streptococcus
thermophilus. The content of the milk sugar in
yogurt is reduced by 20-30%. The remainder sugar
milk serves as a source of energy worth 4.1 kcal.
Yogurt is a rich source of calcium to meet the needs
of man. Calcium maintains volatility of the heart
muscle and has great importance for the proper
functioning of the nervous system , stimulating
effects of endocrine and accelerating blood clots.
Изготвили:
Петър Атанасов – Мишо
Никола Куванджиев